Acute myocardial infarction is a disease in which the blood vessel (coronary artery) for supplying oxygen and nutrients to the heart itself is clogged with a formed thrombus, and blood flow is blocked decreasing the function of the heart. About 40,000 people per year receive treatment for this disease in Japan. Heart disease is the first leading cause of death in Europe and the United States, and is the second leading cause of death following malignant neoplasma (cancer) in Japan, and is on the rise recently due to factors such as westernization of dietary culture and an increase in stress in social life. In recent years, treatment involving reopening of a clogged portion to allow the blood to be reperfused has been conducted, whereby the death rate in hospitals has become 10% or less. In general, as a reperfusion treatment, there are a method of injecting a drug for dissolving a thrombus and a method of expanding a blood vessel narrowed with a thrombus using a PTCA balloon catheter or the like.
It is considered that the cause of a thrombus inside the coronary arteries is as follows: a gap is formed between cells of an inner membrane (vascular endothelium) constituting the blood vessel due to stress, westernization of diet, smoking, drinking, etc.; and a low-density lipoprotein (LDL) is infiltrated through the gap. The infiltrated LDL is oxidized to become oxidized LDL. The body attempts to treat the oxidized LDL, which is a foreign matter, and macrophages gather, whereby endocytosis starts. As a result, a gruel-like substance called lipid core is accumulated between the vascular endothelium and the vascular tunica media and is expanded in a dome shape inside the blood vessel to form atheroma (see FIG. 10). When the lipid core is accumulated exceeding a certain acceptable range, the vascular endothelium in the atheroma portion ruptures. At this time, blood platelets in the blood attempt to repair the rupture portion forming a thrombus. When the thrombus is formed, blood flow in the coronary arteries is blocked. As a result, oxygen and nutrients are not supplied to the heart itself, whereby the function of the heart is lost. If the thrombus thus formed is not removed early for reperfusion, death can result.
Thrombus suction therapy is a therapeutic method of inserting a tubule with a diameter of about 1.5 mm (referred to as a catheter) through a leg or arm to allow the catheter to reach a lesion portion in the coronary arteries, and removing a thrombus itself by suction. According to the thrombus suction therapy, a thrombus causing the blood vessel to be narrowed is itself removed. Therefore, risks involved in conventional methods such as renarrowing of coronary arteries due to a thrombus that is not completely dissolved by a drug and damage caused by excess expansion of a blood vessel, can be avoided.
The above-mentioned catheter for removing a thrombus from inside the coronary arteries is called a thrombus suction catheter, which is used in combination with a suction device. The suction device conventionally includes two kinds: (1) a vacuum pump using a driving force such as electricity, and (2) a syringe. With the vacuum pump, there is a limit to the ability of a pump and a negative pressure maintenance mechanism using a check valve. Up to now, the proximal end of a catheter can produce only 640 mmHg of negative pressure.
Also, a certain degree of strength is required in a catheter so that the wall surface of the catheter is not crushed due to the negative pressure. Furthermore, in order to facilitate a discharge of an aspirated substance from a lesion portion to the outside of a body, it is necessary to maximize the area (opening area) of an opening cross-section. In a conventional catheter, the opening area remains about 0.65 mm2, and the wall thickness for maintaining the strength is 0.15 mm or more. However, if the wall thickness is increased so as to avoid crushing, flexibility of the catheter is impaired. Therefore, in the case where a lesion portion is at a position that is sharply curved (e.g., #3, #4 of the coronary arteries), crossing of the catheter is unsatisfactory, making it impossible to allow the catheter to reach the lesion portion.
The shape of a distal end opening of a catheter is also important for the thrombus suction catheter.
The opening of a conventional thrombus suction catheter is angled about 30° to 45° with respect to a longitudinal axis. However, in the case where the vascular endothelium is expanded in a dome shape due to lipid core as described above, when the distal end of the catheter is cut straight, the surface of a lesion portion cannot be completely covered even if a cut surface is angled with respect to the longitudinal axis of the catheter. Thus, a gap is formed between the expanded lesion portion and the catheter. As a result, the blood flows into the catheter from the distal end of the catheter during suction, and the negative pressure produced by a suction tool cannot be completely transmitted to the lesion portion, i.e., a thrombus or the vascular endothelium of the lesion portion. Thus, sufficient suction cannot be obtained.
The present invention has been made in view of the above, and its object is to provide a thrombus suction catheter with improved suction and crossing, capable of aspirating atheroma and reaching even a lesion portion that is sharply bent.